The invention relates to a vehicle wheel suspension having a suspension spring, by means of which the vehicle body is proportionally supported on a supporting bracket of the wheel suspension. The wheel load acting upon the pertaining wheel as a result of this support is changeable in that the transmission ratio at a shift lever provided in the load path of the support and swivelably disposed at the vehicle body, or an axle carrier with respect to the latter can be changed by way of an actuator. Concerning the state of the art, reference is made particularly to DE 199 23 343 B4, in addition to EP 1 750 956 B1.
In DE 199 23 343 B4, an advantageous measure is described for a variable adjustment of the distance between the vehicle body and the wheel center of the wheel guided by way of the wheel suspension. Accordingly, a shifting between the wheel lift and the lift of the damping member and/or suspension member of the wheel suspension by way of a shift lever swivelably disposed at the vehicle body (“vehicle-body-side”) is provided, in which case, by way of a position change of this shift lever about its swiveling axis, the variable adjustment of the above-mentioned distance can be caused. For the adjustability of the ratio between the shift lever and the damping member and/or suspension member, an intermediate part is provided which, in turn, can be swiveled by way of an actuator. This intermediate part alone already contributes to the fact that this known arrangement requires relatively high expenditures.
In the EP 1 750 956 B1, a similar measure is described for changing the so-called reaction characteristics of the suspension spring/shock absorber assembly, in which case, instead of the shift lever mentioned above, a cranking mechanism is provided. This arrangement has the advantage that the operating direction of the actuator provided for changing the transmission ratio in the above-mentioned cranking device extends approximately perpendicular to the direction of the force effect of the suspension spring/shock absorber assembly, so that the force to be applied by this actuator for changing the transmission ratio is relatively low. However, on the one hand, this cranking mechanism also requires relatively high expenditures and, on the other hand, like the shift lever arrangement mentioned above, has to be designed for absorbing high forces, specifically the wheel load (vertical wheel force) maximally possible at the respective wheel suspension. This requires a relatively massive, and therefore high-expenditure, and heavy construction, which is definitely a disadvantage.
It is an object of the present invention to provide a remedial measure for the above-described problems.
This and other objects are achieved by a vehicle wheel suspension having a suspension spring, by which the vehicle body is proportionally supported on a supporting bracket of the wheel suspension, wherein the wheel load acting upon the pertaining wheel as a result of the support is changeable in that the transmission ratio at a shift lever provided in the load path of the support and swivelably disposed at the vehicle body or an axle carrier with respect to the latter, can be changed by way of an actuator. Parallel to the load path containing the shift lever and a first suspension spring element, an additional load path with a second suspension spring element effective between the vehicle body and the pertaining wheel is provided at this individual wheel suspension.
According to the invention, only a portion of the vertical wheel force or wheel load present at the respective wheel is guided by way of the device permitting a changeable transmission ratio, which device, because of the simple construction, in the present case, as basically known, is designed in the form of a shift lever. In this case, it should be explicitly pointed out the term “shift lever” is to be understood in an abstract sense. This term therefore includes any device by way of which the line of influence of a force path or load path can be shifted and, at which, as a necessary characteristic, the transmission ratio (of this shift lever) can be changed. For the fraction of the wheel load not guided by way of such a shift lever, a further load path is provided according to the invention, in which a suspension spring element is provided, just as it is in the load path guided by way of the shift lever. Accordingly, (at least) two suspension spring elements connected parallel to one another are provided at a wheel suspension according to the invention. This has the effect that the forces to be transmitted, which are present in the respective load path and particularly in the load path containing shift lever, are thereby reduced. However, since the forces are reduced with respect to their amount, a lighter and simpler shaping of the load path containing the shift lever also becomes possible.
When the first suspension spring element acting upon the shift lever is an approximately horizontally aligned coil spring, the latter can be arranged in an installation space that is still somewhat vacant, preferably in the transverse direction of the vehicle in conventional two-track motor vehicles, particularly passenger cars. It may then also be particularly advantageous to support with respect to one another the load paths of the left-side and right-side vehicle wheel suspension, which are guided by way of the respective shift lever. For such an arrangement, a shock absorber, which is supported at the vehicle body or at the axle carrier and has a conventional construction, can then be provided more easily than in the case of the usual stabilizers in the mutually supported load path, whereby a simple damping of rolling motions of the vehicle body will then also easily become possible. This shock absorber is preferably tuned to the intrinsic rolling frequency of the vehicle body.
In this context, it should be pointed out that, by means of a wheel suspension according to the invention with a changeable wheel load in the case of two-track vehicles, the actuators influencing the respective wheel load, for swiveling the shift levers on an axle curing a cornering of the vehicle, can be controlled such that the roll angle of the vehicle body will be limited. As a result, a (transverse) stabilizer, which is otherwise provided at this axle, can be eliminated, and an arrangement according to the invention can take up its installation space.
When a vibration absorber for damping the rolling motion is provided in the mutual support implemented, for example, by way of a suitable rod, which vibration absorber acts upon this rod, for example, suitable stops may be provided which limit the displacement path of the above-mentioned rod in order not to excessively impair the above-mentioned possibility of the roll angle reduction by the suitable control of the actuator or actuators. However, naturally, a vibration absorber may also be provided in the respective load path, in addition to the suspension spring element, without such a mutual support of the load paths of the left and right vehicle side containing the shift lever. This permits not only the desired influencing of the wheel load and thereby also a leveling control of the vehicle body, but higher wheel-related shock absorber forces can also be achieved when the load capacity in the vehicle is changed, so that also a load-dependent vibration damping is provided.
In this context, the basic advantages of a wheel suspension having the characteristics set forth above should briefly be mentioned. Nowadays, particularly superclass vehicles are still using complex systems for desirably influencing the wheel load. These are a pneumatic shock absorption for the leveling, an active roll stabilization for reducing the roll angle and, in top models, full-load-bearing active chassis up to the coupling with stereo cameras in order to be able to react to obstacles in an anticipatory fashion and to correspondingly adapt the wheel load. The necessary infrastructure for such systems has considerable negative effects on the vehicle package, its weight and manufacturing costs, and is connected with considerable power consumption. This, in turn, has a negative effect on the fuel consumption and the exhaust emissions of the vehicle. The control energy required for these customary systems for influencing the wheel load is high, because the respective actuators act in the direction of the load path in the case of the active roll stabilization as well as in the case of a full-load-bearing active chassis, and the adjusting forces are therefore at the level of the stationary wheel load. In the case of the pneumatic shock absorption, the expenditures for the compressor, the air dryer and the pressure accumulator result in unfavorable expenditures.
In contrast, a wheel suspension according to the invention can be designed to be considerably more advantageous, specifically when the operating direction of the actuator, when changing the transmission ratio with the effective force direction of the first suspension spring element provided in the load path containing the shift lever, encloses an angle on the order of from 70° to 110°. Specifically, when the adjusting direction of the actuator is not selected in the direction of the load path but perpendicularly thereto, the actuator, with the exception of friction effects, has to carry out virtually no adjusting work.
A further advantageous development of a wheel suspension according to the invention is characterized in that the transmission ratio at the shift lever can be changed over a wide range by the displacement of the supporting point of the first suspension spring element or a transmission rod supported with its other end at a supporting bracket of the wheel suspension, in that this supporting point can be displaced closely into the surroundings of the bearing point of the shift lever at the vehicle body or axle carrier. Specifically, when the above-mentioned load path with the corresponding positioning of the above-mentioned supporting point were to extend precisely through the above-mentioned bearing point of the shift lever, a transmission ratio of “zero” would be obtained, and the wheel suspension would not be influenced by way of this load path. When, in contrast, the above-mentioned supporting point is moved far away from the bearing point of the shift lever, it can definitely be shown that the support of the wheel load is taken on for the most part by the first suspension spring element and less by the second suspension spring element, which is provided in the other load path that does not contain the shift lever. Between these two extreme positions, virtually any intermediate position is possible, particularly when the above-mentioned supporting point of the first suspension spring element or of the transmission rod can be displaced along a guiding link, and the actuator is provided with a suitable transmission for displacing the supporting point next to this guiding link. Utilizing these possibilities to a maximum, the above-mentioned supporting point may even be displaceable such that the load path can extend by way of the shift lever at both sides of the bearing point of the shift lever at the vehicle body or axle carrier. As a result, a quasi-negative transmission ratio can be adjusted at the shift lever and, as a function of the layout of the suspension spring elements, in the extreme case, the respective wheel can be completely relieved or even be minimally lifted off the ground. For example, in the case of a flat tire, a tire could particularly easily be changed without the aid of a jack. Likewise, in connection with a so-called preview function (for example, by use of a stereo camera), it is contemplated that the respective wheel load is reduced in a targeted manner before driving over a recognized obstacle.
The actuator may be constructed as an electric motor with a self-locking threaded spindle on an output side, whereby undesirable changes of the transmission ratio at the shift lever, for example, under the effect of environmentally caused wheel load fluctuations, can be excluded. In addition, if a wheel suspension according to the invention is provided at a steerable wheel, it is advantageous for the force effect line of the above-mentioned transmission rod between a supporting bracket of the wheel suspension and the shift lever to at least approximately intersect with the steering axle of the steerable wheel. It can thereby practically be excluded that a desired change of the wheel load caused at the shift lever by a change of the transmission ratio will cause a (slight) steering movement of the wheel.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.